How to Solve Investment Problems Part 2

This is the second part of the Solving Investment Problems Series. In thefirst part, we discussed in detail the solution of a problem at two different rates of interest. In this post, we discuss another problem.

Problem

Mr. Reyes invested a part of Php70000 at 3% yearly interest and the remaining part at a 5% yearly interest. The annual interest on the 3% investment is Php100 more than the annual interest on the 5% investment. How much was invested at each rate?

Solution

If we let x be the amount invested at 3%, then, 70000 – x is the amount invested at 5%. The yearly interest is the product of the rates and the amount invested so,